What Is THC-O? The Chemistry, the Law and the Open Questions

Written by the Rose Mary Jane team. Reviewed by our Cannabis Guides. Last updated 9 October 2026.

Quick answer: THC-O is short for THC-O acetate, an acetate ester of THC made in a lab by reacting THC with acetic anhydride. The DEA says it does not occur naturally in the cannabis plant. We do not sell it, because Maine adult-use stores can only stock products from the state's licensed and tested supply chain.

Key takeaways:

• THC-O acetate is a semi synthetic acetate ester of THC, not a plant cannabinoid.

• The DEA stated in February 2023 that delta-8 and delta-9 THC-O are Schedule I.

• A federal appeals court read the hemp law differently in September 2024.

• Portland State researchers detected ketene in vaped cannabinoid acetates in 2022.

• Maine adult-use products must pass a mandatory testing panel before sale.

THC-O at a glance: what is it and where does it come from?

THC-O acetate is THC with an acetate group attached to it, made in a lab rather than grown in a plant. Chemically it is an acetate ester, with the formula C23H32O3 and a molar mass of about 356.5 grams per mole. It comes in two versions, named after whether the starting material was delta-8 THC or delta-9 THC.

It is often described as a prodrug, meaning the body has to break off the acetate group before the THC itself is active.

Here is how it compares with the delta-9 THC in a licensed Maine product.

How is THC-O actually made?

By acetylation, which means adding an acetate group to a molecule that already exists. Historical descriptions of THC-O involve acetylating cannabis extracts with acetic anhydride.

That is the same class of reaction used to make other acetate esters, and acetic anhydride is a controlled industrial reagent. We are not going to publish conditions, and no reputable source does.

The point for a reader is simple. The acetate group is not something the plant puts there. It is added afterward, in a lab, to a starting material that was itself often converted from CBD. Hemp THC drinks versus dispensary THC drinks covers that conversion chain in more detail.

Is THC-O found in the cannabis plant?

Not in any meaningful quantity, and the clearest statement on that comes from the DEA itself. Terrence L. Boos of the DEA's Drug and Chemical Evaluation Section set it out in a letter dated 13 February 2023. Delta-9 THC-O and delta-8 THC-O "do not occur naturally in the cannabis plant and can only be obtained synthetically," he wrote.

That matters for more than chemistry. The 2018 Farm Bill definition of hemp turns on what comes from the plant, so a compound made only by synthesis sits awkwardly inside it.

The historical court cases involving THC-O all concerned acetylated extracts, not plant material. Nobody has reported finding it in flower.

Is THC-O really three times stronger than delta-9?

That claim comes from sellers, not from published research. The National Capital Poison Center covers it in an article by Kelly Johnson-Arbor and William Troutman. They note that sellers claim it is three times more potent than delta-9 THC, and that it has psychedelic actions. They say published studies have not produced results that would support either claim.

The evidence that does exist is thin and old. The potency figure usually cited traces back to US Army Edgewood Arsenal work. That was reported as about twice the capacity to produce ataxia as THC in dogs. It is cited secondhand in a 1984 National Research Council volume. No dose, sample size or method was published with it.

So the honest answer is that nobody has published a reliable human potency comparison. The Poison Center also says plainly that there is no standardized dosing of delta-9 THC-O acetate for humans.

Is THC-O a psychedelic?

The survey evidence says no. Daniel Kruger of the University at Buffalo published a study in the Journal of Psychoactive Drugs in 2023, with nearly 300 participants who had used THC-O-acetate.

Asked directly, 79 percent said the experience was "not at all" or "a little" like a psychedelic experience. Their scores fell well below the threshold for a complete mystical experience on the questionnaire used.

Kruger's own summary of the question was blunt. Asked whether there really is a psychedelic cannabinoid, he said the answer is not so much.

What did the Portland State ketene research find?

It found ketene, a toxic gas, in the vapor from heated cannabinoid acetates. Kaelas Munger, Robert Jensen and Robert Strongin of Portland State University published "Vaping Cannabinoid Acetates Leads to Ketene Formation" in Chemical Research in Toxicology in 2022.

They tested three cannabinoid acetates, including a THC acetate, plus a commercial THC acetate product bought online. Ketene turned up consistently in the vaped condensates from all of them. Portland State reported that it formed at lower temperature settings than previously thought.

The researchers were careful about what they had not shown. Munger noted the results came from a single puff. He said the real concern is prolonged exposure, and that nobody knows yet what that exposure is. Strongin said ketene is virtually untraceable in the human body, because it reacts strongly with biological molecules.

We will stay inside that. The published finding is that vaping these acetates forms ketene, and the researchers themselves say the long term picture is unstudied. We are not going to stretch it further than they did.

Is THC-O legal, and what does the DEA say?

The federal position is disputed, and anyone telling you it is settled is overselling. Two documents matter.

The DEA's February 2023 letter concluded that delta-9 THC-O and delta-8 THC-O are tetrahydrocannabinols controlled in Schedule I by 21 U.S.C. section 812(c), along with products containing them.

Then on 4 September 2024, the US Court of Appeals for the Fourth Circuit took a different view. The case was brought by Tonya Anderson against Diamondback Investment Group. The court held that THC-O meets the Farm Bill definition of hemp. It said the statute was clear enough to read on its own, and that it need not defer to the DEA.

So one federal agency says one thing and one federal appeals court says another. That is an unresolved conflict, not a green light.

Why does a licensed Maine store not sell THC-O?

Because our license only lets us sell what Maine's own system produced and tested. That is the whole answer, and it has nothing to do with disapproval.

The Maine Office of Cannabis Policy, which sits inside the Department of Administrative and Financial Services, regulates adult-use cannabis under Title 28-B M.R.S. and rules at 18-691 CMR. Since 1 October 2021, products moving between licensees have had to pass mandatory testing. OCP lists the required categories. They cover filth and foreign material, dangerous molds and mildews, and harmful microbes. They also cover THC potency, homogeneity and cannabinoid profile, plus water activity and moisture content. Metals including cadmium, lead, arsenic and mercury are on the panel, along with residual solvents.

THC-O is not produced inside that chain, so there is no compliant path onto our shelf. There is also no state potency standard for it, which means no label we could print that would mean anything. How to read a Maine cannabis label shows what we are required to put on a package.

One thing we will not do is tell you that what we sell is safe. We cannot. What we can say is what it is, where it came from and what the lab measured.

What can you buy instead, and who should skip all of this?

Start by telling us what you were actually after. Most people asking about THC-O want one of three things, and tested products cover all three.

• More intensity. A concentrate or an infused pre-roll with a verified potency number does that.

• A different character of effect. Look at products with CBN, CBG or THCV on the certificate.

• Novelty. Fair enough, but novelty from an untested supply chain is a different trade.

Our guides to types of cannabis concentrates, infused pre-rolls and minor cannabinoids like CBN, CBG and THCV are the places to start.

Some people should skip novel cannabinoids altogether. Anyone under 21. Anyone who is pregnant or nursing. Anyone on prescription medication who has not asked a provider. Anyone who gets drug tested for work. And anyone who wants a product for a health reason, which is a conversation for a clinician, not a shop. Whether you need a medical card in Maine explains how the two programs differ.

Frequently asked questions

Is THC-O the same thing as delta-8?

No. Delta-8 THC is a cannabinoid that occurs in the plant in small amounts, though most sold is converted from CBD in a lab. THC-O acetate is a different thing again. It is an acetate ester made by reacting THC with acetic anhydride, and the DEA says it does not occur naturally in the plant. Confusingly, THC-O is sold in both delta-8 and delta-9 versions, named after whichever THC it was made from.

Is THC-O legal in Maine?

The federal position is contested and we are not going to pretend otherwise. The DEA said in a letter dated 13 February 2023 that delta-8 and delta-9 THC-O are Schedule I controlled substances. In September 2024 the Fourth Circuit read the 2018 Farm Bill differently and said it need not defer to the DEA. Separately, Maine's adult-use program only allows products from its own licensed and tested supply chain, which THC-O is not part of.

Can you buy THC-O at a licensed Maine store?

Not at ours, and you should not expect to find it at any Maine adult-use store. Everything on our shelves has to come from a licensed Maine cultivator or manufacturer and pass the state's mandatory testing panel. THC-O is made outside that system, so there is no compliant route onto the shelf. If you see it for sale somewhere in Maine, that seller is not operating under the adult-use program we are licensed under.

Is THC-O three times stronger than regular THC?

That is a seller's claim, not a finding. The National Capital Poison Center notes that online sellers claim it is three times more potent than delta-9 THC, and says published studies have not produced results that would support that claim. The older data point often cited traces to US Army Edgewood Arsenal work, reported as about twice the capacity to produce ataxia as THC in dogs, with no published dose or sample size.

What did researchers find about vaping THC-O?

Kaelas Munger, Robert Jensen and Robert Strongin of Portland State University published Vaping Cannabinoid Acetates Leads to Ketene Formation in Chemical Research in Toxicology in 2022. They detected ketene, a toxic gas, in the vaped condensates of three cannabinoid acetates and in a commercial product bought online. Munger said the results came from a single puff and that long term exposure is the real unknown. Strongin said ketene is virtually untraceable in the body.

What should I buy instead of THC-O?

Tell us what you were hoping it would do and we will match it from tested stock. If you wanted a stronger effect, a concentrate or an infused pre-roll will get you there with a known potency number on the label. If you were after a different quality of effect, look at products with CBN, CBG or THCV on the certificate. Either way the milligrams are printed and the batch was tested.

Bring the question to the counter

If you have read this far, you are the kind of customer our Cannabis Guides like. Come in to 327 St John St and ask. We would rather spend ten minutes on a certificate of analysis with you than sell you something you are unsure about.

You can look at what is in stock on the Rose Mary Jane menu first, and our Portland store page has the hours. If it is your first time in a shop, what to expect at a dispensary walks through it, and Maine possession and purchase limits covers how much you can buy. If you want something low key to start with, our THC mocktail builds use tested drinks and tinctures.